Later in the film, it explains that he too was once a human, before his parents discarded him as a baby and he became a demigod. But if he was a human before he became a demigod, how did he live without the islands, fire, or the sun?

Is he just exaggerating his feats, or is it a flaw the writers overlooked?

Because reality gets in the way of a good story/it's a cartoon.
– SnowMar 27 '17 at 10:53

@Pete: Barring a good story, Maui is based on a well established mythological figure who is claimed to have actually done all these things. Although the movie simplifies the story in favor of storytelling, Maui is told to have done all these things in the original myth.
– FlaterMay 30 '17 at 15:29

2 Answers
2

Maui wants to be praised by the human, and be known as a hero, which is why he does all these feats in the first place. So it's not unlikely that he is exaggerating to some degree.

But even if it's all true, that doesn't mean humans couldn't exist before. He lassoed the sun to stretch the day, there was still a sun and days before that. And even if he raised islands, doesn't mean he raised every island, so there could be islands before.

Maui is also based on real Polynesian myths (see Māui (mythology) on wikipedia). Most, if not all, of his feats are taken from these myth, so if you want to know more about his origin and what he's done, you can read more about it.